1. Field of the Invention
The present invention relates to a rear-focus optical system, an imaging apparatus, and a method for focusing the rear-focus optical system.
2. Related Background Art
There have been proposed a lot of so-called Gaussian type lenses having substantially symmetrical power distribution with respect to an aperture stop as a large-aperture standard lens used for a film camera and a still video camera in, for example, Japanese patent Application Laid-Open No. 1-155310. In such a Gaussian type lens, there have been announced various proposals in which correction of variation in optical performance upon varying focusing from an object locating at infinity to an object locating at a close distance is carried out. Moreover, there has been proposed a so-called retrofocus type standard lens in which strong negative refractive power is disposed to the object side of the aperture stop deforming a symmetrical power distribution of a Gaussian type.
However, conventional lenses described above have a problem that the dimension of the lens is not sufficiently compact.